JP3174577B2 - Current distribution between each strand of superconducting winding - Google Patents

Description

Description: TECHNICAL FIELD In applying the superconductivity effect, a cooling object is usually
It is stored in a so-called cooling tank. The electrical conductor of the cooling object in this application consists of a series of winding strands. The lower part of the cooling tank contains a refrigerant in the form of a cryogenic liquid surrounding a cooling object. The space above the liquid level of the cooling tank is filled with a gaseous refrigerant. The current connection to the cooling object is made by current leads in the bush. The bush is attached to the lid of the cooling tank via a fixing flange. The present invention relates to a connection structure between a winding strand and an ac current lead wire, and relates to a technique for appropriately distributing current between the strands.

BACKGROUND OF THE INVENTION Problems and Reactors Conductors or transformer windings of a reactor are often divided into a plurality of insulated strands in order to minimize the undesirable effect of skin effect. When many of the strands intersect, there is always some variation in the induced voltage because the individual strands do not surround the magnetic flux exactly exactly. For this reason, the current distribution between each strand becomes uneven,
The so-called copper loss increases. However, since the maximum current flows through the strand where the induced voltage is maximum and the resistance voltage drop is also maximum, the effect of stabilizing the current distribution is obtained by the resistance of the strand.

By the way, if such a winding is composed of a plurality of superconducting strands, the stabilization resistance voltage drop is negligible. For example, IEEE TRANSACTI issued in January 1992
Referring to the article of ONS ON MAGNETS, Vol. 28, No. 1, titled `` Improvement of Large-Capacity Superconducting Cable for 1000 kVA Class Power Transformer '', the prior art was electrically connected to each other at the terminal position of the winding. A winding strand is provided. Due to the variation in the induced voltage, a large variation also appears in the current distribution. The strands that need to carry the most current run the risk of losing their superconducting capabilities due to too high a critical current density. This causes local heat generation.

However, for example, such a problem does not occur in a dc device equipped with a superconducting strand used in combination with a magnet.
In the steady state, a voltage that disturbs the current distribution is not induced, and the current changes under a very small change in the time ratio.

Problems associated with superconducting applications include influx into the cryogenic liquid caused by temperature differences between the surroundings and the cooling body. This problem is due to the fact that the current leads of the bush as well as good electrical conductors are also good heat conductors. Furthermore, at least under large currents, the current flowing through the current leads generates heat in the current leads of the bush. This generation of electrical heat is caused by the ohmic resistance of the current leads. In the case of alternating current, an eddy current is induced to generate heat. It is also necessary to consider the increase in resistance caused by the skin effect. The gas generated by the inflow of heat into the cooling tank can freely flow out into the surrounding air from the opening of the bush portion arranged outside the cooling tank.

What this means is that in the process of moving to the lid and discharging to the surroundings to reach the surrounding air temperature, the gas flow is at the boundary between the liquids and the gas, while maintaining the temperature of the liquid as much as possible while maintaining the temperature of the liquid as much as possible. Because it flows around, it can be used for cooling the current leads. This gas flow cooling is often referred to as counterflow cooling because the direction of the gas flow is opposite to the direction of heat flow. In order to maximize this effect, the current leads are designed as heat exchangers. The current leads themselves located in the gas-filled location of the cooling tank can have a variety of structures. "Superconducting Magnets" Clarendon Press, Oxford 19
In 1983, page 272, the current leads are described as foils electrically connected in parallel. These foils are installed at an arbitrary distance from each other, and form a refrigerant passage along the foil. The foil assembly is arranged in a cylindrical surrounding casing made of an insulating material. The peripheral casing has an inner opening space having a rectangular cross section. A patent application filed concurrently with the present application and entitled "Gas cooled bush used for superconductivity" by the same applicant,
A cooling device that utilizes a gas flow to cool a current lead is described. The current leads, in this example, consist of a number of plate-like sub-leads with insulated intermediate lateral ribs. Outside the cooling tank, the sub-leads have turned into integrated current leads. In particular, according to the conventional example described in "Superconducting magnet", the sub-leads are electrically interconnected at the terminals of the winding.

SUMMARY OF THE INVENTION AND ADVANTAGES As is evident from the foregoing, the non-superconductor has a current distribution between the closed circuits of each strand connected to each other at the terminal position of the winding due to the resistive voltage drop generated in the strand. It plays a stabilizing effect. On the other hand, if the strand is made of a superconductor, the stabilizing effect is negligible.

Thus, according to the above arrangement, the current leads in the bush are divided into a number of sub-leads in the form of foils or plates, for cooling reasons and to minimize the effects of the skin effect. These sub-leads are connected to one another at the terminal positions of the windings for all the strands of the winding. As is evident from the above, a certain amount of electric heat is generated in the current lead of the sub-lead of the bush due to the ohmic resistance.

The present invention provides that the current leads of the bushing are provided with a number of mutually insulated sub-leads in the form of foils or plates, commensurate with the mutually insulated strands provided in the winding, and Is connected to a sub-lead of each current lead of the bush. The electrical interconnection of the winding strands occurs directly above the cooling tank, where the sub-leads turn into integral conductors. In this manner, a strand circuit, ie, a circuit made from the strands and each sub-lead, is two stranded from the sub-lead.
It has a certain amount of ohmic resistance across the two current leads. This further implies that in a winding having a superconducting strand, a stabilizing effect acts on the current distribution between the strands.

Since the winding is composed of a number of superconducting strands, it is not practical to install as many sub-leads on the current leads of the bush as the winding strands. Accordingly, the present invention divides the number of winding strands into the same number of groups as the sub-leads included in the current leads of the bushing, so that each group can have the same number of strands. This means that under such circumstances, the current distribution has a considerable current stabilizing effect.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a sectional view of a cooling tank showing an embodiment of a connection structure inside the cooling tank.

FIG. 2 shows a modification of the connection structure inside the cooling tank according to the present invention.

FIG. 3 is a sectional view showing the current leads of the cooling tank along a plane orthogonal to the sectional views of FIGS. 1 and 2.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Generally, the cooling object is selected in its shape and size so that the electric conductor attached to the cooling object is brought into a superconducting state. Change. The bush with the current leads is typically installed in practice on the lid of the cooling tank. However, the position of the lid on which the bush is installed can be determined depending on the cooling object used.

1 and 2 show a cross section of a cooling tank in which a bush is arranged in the center of a lid. The illustrated cooling tank comprises an embodiment with two current leads and comprises a cooling tank 1, a lid 2, a cooling object 3, a cross strand and a yoke 3b, for example windings 3a in the form shown, cryogenic Shown are a liquid 4, a gaseous coolant 5, current leads 6 and 7, a bushing casing 8 surrounding a current lead with a fixing flange 9, and an opening 10 for gas discharge.

Further, these figures show an insulator 11 interposed between the current leads. The current lead is composed of a number of plate-shaped sub-leads 12. These sub-leads are held above the cooling tank and form a substantially integrated current lead. For cooling and other reasons, it is desirable to keep the sub-leads at a predetermined distance from each other inside the cooling tank. As is apparent from the drawing, a method is devised to make the distance between the sub-leads equal, form a cooling passage in the gap between the respective sub-leads, and improve the mechanical stability. A plurality of rows of insulating material lateral ribs 13a, 13b, ... 13n are arranged between the sub-leads of the current lead 6. Similarly, the inclined lateral ribs are also provided between the sub-leads of the current lead 7.
14a, 14b,... 14n are arranged. The location of the lateral ribs and cooling channels is evident from FIG. 3 looking at the current leads in a plane perpendicular to the plane along FIGS. 1 and 2.

In the preferred embodiment according to FIG. 1, the winding consists of the same number of strands as the sub-leads included in the current leads of the bush. That is, one strand is connected to the end of each sub-lead. However, the strands are not electrically interconnected until the sub-leads are connected together outside the cooling tank by the transverse insulating ribs between the sub-leads.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-48-69081 (JP, A) JP-A-48-77786 (JP, A) JP-B-52-18911 (JP, B1) US Pat. , A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01F 30/00-38/42 H01B 12/00-13/00

Claims (3)

(57) [Claims] An alternating current is supplied, said current being supplied between the current leads (6, 7) and the strands of the superconducting winding (3a) through the ends of the current leads, The windings are arranged in the lower part (4) of the cooling tank filled with coolant and each part of the current leads arranged in the upper part (5) of the gas-filled cooling tank consists of a main insulator (11). And are configured as plate-shaped sub-leads (12), wherein the sub-leads have no intermediate insulator outside the cooling tank and are held together as integral conductors in a cooling tank. Inside, a number of rows of insulating lateral ribs (13a, 13b, ... 13n, 14a, 14b, ... 14n) are arranged between the sub-leads, and the strands are connected to the ends of the sub-leads. Superconducting winding characterized by Connecting structure between the strands. 2. The connection between the strands of a superconducting winding according to claim 1, wherein an alternating current is supplied and the current supply takes place through the current leads and the ends of the current leads. A connection between the strands of a superconducting winding, wherein each strand is connected to its own sub-lead. 3. The connection between the strands of a superconducting winding according to claim 1, wherein an alternating current is supplied, said current being supplied through current leads and the ends of said current leads. A connection structure between superconducting winding strands, characterized in that the strands are divided into groups of equal size corresponding to the number of sub-leads, each group being connected to its own sub-lead.